Stainless wrought and cast materials and welding additives for structural units exposed to hot, concentrated sulfuric acid

Abstract

In the processing of hot concentrated sulfuric acid or oleum in steel apparatus, the improvement wherein said apparatus is formed of an alloyed material comprising an iron-chrome-nickel-silicon alloy containing 13 to 32% by weight Cr, 5 to 25% by weight nickel and 4 to 9% by weight Si and having a structure containing more than 10% delta-ferrite.

What is claimed is: 
     
       1. In the processing of hot concentrated sulfuric acid or oleum in steel apparatus, the improvement wherein said apparatus is formed of an alloyed material comprising an iron-chrome-nickel-silicon alloy containing 13 to 32% by weight Cr, 5 to 25% by weight nickel and 4 to 9% by weight Si and having a structure containing more than 10% delta-ferrite, wherein the steel at most contains the following percentages by weight of the indicated component: Mn 8%, Mo 3%, Cu 4%, Ag 2%, Co 20%, W 4%, Nb/Ta together 2% and N 0.2%. 
     
     
       2. The process according to claim 1, wherein the acid being processed is sulfuric acid of at least 75% concentration and it is processed at a temperature of at least about 90° C. 
     
     
       3. The process according to claim 1, wherein the acid being processed is sulfuric acid of at least 85% concentration and it is processed at a temperature of at least about 150° C. 
     
     
       4. The process according to claim 1, wherein the acid being processed is sulfuric acid of at least 90% concentration and it is processed at a temperature of at least about 200° C. 
     
     
       5. The process according to claim 1, wherein the processing is effected at a pressure from about 0.1 to 10 bar.